CN110709434B - Process for preparing ethylene-vinyl acetate copolymer - Google Patents
Process for preparing ethylene-vinyl acetate copolymer Download PDFInfo
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- CN110709434B CN110709434B CN201980002312.7A CN201980002312A CN110709434B CN 110709434 B CN110709434 B CN 110709434B CN 201980002312 A CN201980002312 A CN 201980002312A CN 110709434 B CN110709434 B CN 110709434B
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- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2/00—Processes of polymerisation
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- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F218/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an acyloxy radical of a saturated carboxylic acid, of carbonic acid or of a haloformic acid
- C08F218/02—Esters of monocarboxylic acids
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- C08F218/08—Vinyl acetate
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- C08F2/00—Processes of polymerisation
- C08F2/01—Processes of polymerisation characterised by special features of the polymerisation apparatus used
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Abstract
A method for producing an ethylene-vinyl acetate copolymer, wherein the ethylene-vinyl acetate copolymer is continuously produced in a polymerization tank containing a reaction liquid containing ethylene, vinyl acetate, a polymerization initiator, and methanol, and the polymerization tank is connected to a heat exchanger for circulating a refrigerant via a pipe; the method is characterized by comprising the following steps: supplying ethylene, a polymerization initiator and methanol to the polymerization vessel; introducing a pressurized gas containing ethylene present in the gas phase portion of the polymerization vessel into the heat exchanger; supplying vinyl acetate cooled to-50 to 23 ℃ to the upper part of the heat exchanger; a step in which ethylene is absorbed in the vinyl acetate while flowing down in the aforementioned heat exchanger; a step of introducing vinyl acetate in which ethylene is dissolved from the bottom of the heat exchanger and adding the vinyl acetate to the reaction solution in the polymerization vessel; and a step of taking out the reaction solution from the polymerization vessel. Thus, a method for efficiently removing heat when polymerizing an ethylene-vinyl acetate copolymer is provided.
Description
Technical Field
The present invention relates to a process for the preparation of ethylene-vinyl acetate copolymers.
Background
An ethylene-vinyl alcohol copolymer (hereinafter, sometimes referred to as EVOH) is a thermoplastic resin excellent in gas barrier properties, fuel barrier properties, chemical resistance, stain resistance, non-charging properties, mechanical strength, and the like. Further, the molded article is molded into the form of a film, a sheet, a bottle, a cup, a tube, a pipe, or the like by utilizing such characteristics, and is used for various applications including packaging containers. EVOH is generally produced by saponifying an ethylene-vinyl acetate copolymer (hereinafter, sometimes referred to as EVA), and a method for efficiently producing high-quality EVA is required.
EVA is produced by copolymerizing ethylene and vinyl acetate, but the polymerization reaction is exothermic, and therefore it is necessary to remove the heat of polymerization from the reaction liquid. Various methods have been proposed so far for efficiently removing the heat of polymerization from the reaction solution.
Patent document 1 describes a method of continuously polymerizing EVA under conditions in which the heat transfer area of the jacket and/or coil and the amount of polymerization heat satisfy a specific relationship, using a polymerization tank having a cooling means using the jacket and/or coil. However, when a cooling jacket is used, it is difficult to increase the contact area between the inner wall of the polymerization vessel to be cooled and the reaction solution, and there is a problem that the heat removal efficiency is reduced as the capacity of the polymerization vessel is increased. On the other hand, in the case of using a cooling coil, the heat removal efficiency is easily improved by increasing the contact area with the reaction solution, but a retention portion is easily formed in the reaction solution, and a deteriorated polymer may be generated in the retention portion. Further, even when both the sheath and the coil are used, since a part of the reaction solution is at a low temperature, the viscosity of the part is inevitably increased, and the retention of the reaction solution is promoted.
On the other hand, patent document 3 describes a method in which a cooling coil is provided outside the ceiling of a polymerization tank, and EVA is continuously polymerized while cooling the ceiling. In this case, although the problem of scale adhesion is hard to occur, it is not easy to increase the ceiling area, and it is unavoidable that the heat removal efficiency is reduced as the capacity of the polymerization tank is increased.
Patent document 4 describes a method of introducing vinyl acetate into a heat exchanger when continuously polymerizing EVA in a polymerization solution containing ethylene, vinyl acetate, methanol, and a polymerization initiator, absorbing ethylene taken out of a polymerization tank with vinyl acetate in the heat exchanger, and then introducing vinyl acetate in which ethylene is dissolved into the polymerization tank. At this time, the flow of vinyl acetate and the flow of ethylene in the heat exchanger are in counter-current contact. This allows the heat exchanger to remove not only the latent heat of dissolution of ethylene but also the vinyl acetate, and thus it is believed that heat can be efficiently removed. However, the heat removal efficiency thereof is still insufficient in some cases. Further, when the ethylene-containing gas rises in the heat exchanger, the vinyl acetate flowing down is lifted, so-called flooding phenomenon occurs in which the vinyl acetate is blown up to the upper part in the heat exchanger, and stable production is sometimes hindered.
Documents of the prior art
Patent document
Patent document 1: japanese laid-open patent publication No. 2002-128807
Patent document 2: japanese patent laid-open publication No. 2002-356517
Patent document 3: japanese laid-open patent publication No. 11-116637
Patent document 4: japanese laid-open patent publication No. 60-53513
Patent document 5: japanese patent laid-open publication No. 2002-338607.
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for efficiently removing heat when polymerizing EVA.
Means for solving the problems
The above object is achieved by providing a method for producing an ethylene-vinyl acetate copolymer, wherein the ethylene-vinyl acetate copolymer is continuously produced in a polymerization tank containing a reaction liquid containing ethylene, vinyl acetate, a polymerization initiator, and methanol, and the polymerization tank is connected to a heat exchanger through piping for circulating a refrigerant; the method is characterized by comprising the following steps:
supplying ethylene, a polymerization initiator and methanol to the polymerization vessel;
introducing a pressurized gas containing ethylene present in the gas phase portion of the polymerization vessel into the heat exchanger;
supplying vinyl acetate cooled to-50 to 23 ℃ to the upper part of the heat exchanger;
a step in which ethylene is absorbed in the vinyl acetate while flowing down in the aforementioned heat exchanger;
a step of introducing vinyl acetate in which ethylene is dissolved from the bottom of the heat exchanger and adding the vinyl acetate to the reaction solution in the polymerization vessel; and
and a step of taking out the reaction solution from the polymerization vessel.
In this case, a preferable embodiment is a method in which the pressurized gas containing ethylene is supplied to the upper part of the heat exchanger, and the pressurized gas containing ethylene is brought into co-current contact with vinyl acetate in the heat exchanger. In addition, a preferred embodiment is a method in which a pressurized gas containing ethylene is supplied to a lower portion of the heat exchanger, and the pressurized gas containing ethylene is brought into counter-current contact with vinyl acetate in the heat exchanger.
In the above production method, it is preferable that vinyl acetate cooled to-50 to 10 ℃ is supplied to the upper part of the heat exchanger. It is also preferable that the ethylene content of the ethylene-vinyl acetate copolymer obtained is 15 to 55 mol%. Further, it is preferable that the heat exchanger is a wetted wall heat exchanger.
Effects of the invention
According to the production method of the present invention, heat can be efficiently removed when polymerizing EVA, and the production capacity can be improved without greatly modifying the apparatus.
Drawings
[ FIG. 1] an EVA polymerization apparatus used in examples 1 to 8.
[ FIG. 2] EVA polymerization equipment used in examples 9 to 16.
Detailed Description
The present invention is a method for producing an ethylene-vinyl acetate copolymer, wherein an ethylene-vinyl acetate copolymer is continuously produced in a polymerization tank containing a reaction liquid containing ethylene, vinyl acetate, a polymerization initiator, and methanol; the method is characterized by comprising the following steps:
supplying ethylene, a polymerization initiator and methanol to the polymerization vessel;
introducing a pressurized gas containing ethylene present in the gas phase portion of the polymerization vessel into the heat exchanger;
supplying vinyl acetate cooled to-50 to 23 ℃ to the upper part of the heat exchanger;
a step in which ethylene is absorbed in the vinyl acetate while flowing down in the aforementioned heat exchanger;
a step of introducing vinyl acetate in which ethylene is dissolved from the bottom of the heat exchanger and adding the vinyl acetate to the reaction solution in the polymerization vessel; and
and a step of taking out the reaction solution from the polymerization vessel.
The present invention relates to a method for continuously producing an ethylene-vinyl acetate (EVA) copolymer in a polymerization tank containing a reaction liquid containing ethylene, vinyl acetate, a polymerization initiator, and methanol. Here, methanol is a solvent, and EVA is prepared by copolymerizing ethylene and vinyl acetate in a methanol solution in the presence of a polymerization initiator. In order to prepare EVA continuously, the above steps are performed simultaneously in parallel. Further, methanol functions as a chain transfer agent, and the degree of polymerization of the EVA obtained can be controlled by adjusting the amount of methanol added.
The reaction liquid in the polymerization tank contains ethylene, vinyl acetate, a polymerization initiator, and methanol, and ethylene and vinyl acetate are copolymerized to obtain an ethylene-vinyl acetate copolymer. When EVA is polymerized, a copolymerizable monomer other than vinyl acetate and ethylene may be supplied simultaneously for copolymerization. Examples of the monomer include α -olefins such as propylene, n-butene, isobutylene, 4-methyl-1-pentene, 1-hexene, and 1-octene; unsaturated carboxylic acids such as itaconic acid, methacrylic acid, acrylic acid and maleic acid, salts thereof, partial or complete esters thereof, amides thereof, and anhydrides thereof; vinyl silane compounds such as vinyltrimethoxysilane; an unsaturated sulfonic acid or salt thereof; an alkanethiol; vinyl pyrrolidone, and the like.
The polymerization initiator is not particularly limited, and at least 1 selected from the group consisting of a diacyl peroxide-based initiator, a valeronitrile-based initiator, and a peroxydicarbonate-based initiator is suitably used. Examples of the diacyl peroxide-based polymerization initiator include acetyl peroxide, dipropyl peroxide, isobutyryl peroxide, benzoyl peroxide, and dilauroyl peroxide, examples of the valeronitrile-based polymerization initiator include 2,2' -azobis (2,4,4' -trimethylvaleronitrile), 2' -azobis (2, 4-dimethylvaleronitrile), 2' -azobis (4-methoxy-2, 4-dimethylvaleronitrile), 2' -azobis (4-ethoxy-2, 4-diethylvaleronitrile), 2' -azobis (4,4' -diethoxy-2-methylvaleronitrile), and examples of the peroxydicarbonate-based polymerization initiator, examples thereof include dicyclohexyl peroxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, and di-n-propyl peroxydicarbonate. Among these, acetyl peroxide, 2 '-azobis (4-methoxy-2, 4-dimethylvaleronitrile), di-n-propyl peroxydicarbonate and dicyclohexyl peroxydicarbonate are preferable, and 2,2' -azobis (4-methoxy-2, 4-dimethylvaleronitrile) is more preferable.
The temperature of the reaction solution in the polymerization vessel is preferably 40 to 80 ℃. If the reaction temperature is too low, the production efficiency is lowered. The reaction temperature is more suitably above 50 ℃. On the other hand, if the reaction temperature is too high, heat removal becomes difficult, the polymerization reaction is out of control, or the resulting EVA resin is colored. The reaction temperature is more preferably 70 ℃ or lower.
The pressure in the polymerization vessel is preferably 1.5 to 8 MPa. The higher the pressure in the polymerization vessel, the higher the ethylene content of the EVA can be obtained. In order to obtain an EVOH having a good gas barrier property, it is preferable to prepare EVA having a small ethylene content. From this viewpoint, the pressure in the polymerization vessel is more preferably 6MPa or less, and still more preferably 5MPa or less. Further, since the heat removal efficiency decreases as the pressure in the polymerization vessel decreases, it is important to supply cooled vinyl acetate to the heat exchanger according to the present invention. On the other hand, in order to obtain an EVOH having excellent flexibility, it is preferable to prepare EVA having a large ethylene content. From this viewpoint, the pressure in the polymerization vessel is more preferably 2MPa or more, still more preferably 2.5MPa or more, and particularly preferably 3MPa or more. Further, the higher the pressure in the polymerization vessel is, the more easily ethylene is absorbed by vinyl acetate in the heat exchanger, and the heat removal effect is large.
The method for producing EVA of the present invention includes a step of supplying ethylene, a polymerization initiator, and methanol to a polymerization tank. These raw materials are preferably supplied into the polymerization vessel from a conduit directly connected to the polymerization vessel. The raw material is introduced into the polymerization vessel per unit time in a proportion of preferably 8 to 60 parts by mass of ethylene, 0.5 to 25 parts by mass of methanol and 0.001 to 0.05 part by mass of a polymerization initiator with respect to 100 parts by mass of vinyl acetate.
The method for producing EVA of the present invention has a step of introducing pressurized gas containing ethylene present in the gas phase portion of the polymerization tank into a heat exchanger. Further, the method comprises a step of supplying vinyl acetate cooled to-50 to 23 ℃ to the upper part of the heat exchanger. Thereby, the cooled vinyl acetate and the pressurized gas containing ethylene are supplied to the heat exchanger, and are contacted with each other inside thereof. The temperature of vinyl acetate supplied to the upper part of the heat exchanger is-50 to 23 ℃. From the viewpoint of heat removal efficiency, the temperature of vinyl acetate is preferably 10 ℃ or lower, more preferably 5 ℃ or lower, still more preferably 0 ℃ or lower, and particularly preferably-5 ℃ or lower. On the other hand, cooling to less than-50 ℃ increases the equipment cost and the like. From this viewpoint, the temperature of vinyl acetate is preferably-40 ℃ or higher, more preferably-30 ℃ or higher. The method for cooling vinyl acetate is not particularly limited, and a heat exchanger or the like for circulating a refrigerant can be used.
It is also possible to supply a part of the vinyl acetate directly to the polymerization tank without passing through the heat exchanger, but the heat removal efficiency may be lowered. The amount of vinyl acetate fed directly to the polymerization tank is preferably less than half the total amount of vinyl acetate, more preferably less than 1/4. A particularly suitable way is that substantially all of the vinyl acetate is fed to the heat exchanger. When supplying vinyl acetate to the heat exchanger, other components such as methanol may be contained, but the content (mass) of the other components is preferably less than that of vinyl acetate, more preferably less than half of that of vinyl acetate. A particularly suitable way is to feed the heat exchanger substantially free of components other than vinyl acetate.
The preparation method of the EVA of the invention comprises the following steps: a step in which vinyl acetate absorbs ethylene while flowing down in the heat exchanger. A refrigerant cycle is preferred in the heat exchanger to remove heat from the ethylene-absorbed vinyl acetate. At this time, the heat can be extracted from the reaction system by cooling the vinyl acetate in the heat exchanger to extract sensible heat. Further, the vinyl acetate absorbs ethylene to generate latent heat of condensation of ethylene, and thus can also extract heat from the reaction system. That is, the heat exchanger can extract both the latent heat of condensation by ethylene and the sensible heat of cooling by vinyl acetate. In this case, theoretically, both the latent heat of condensation of ethylene and the latent heat of dissolution of ethylene in vinyl acetate are generated, but the latter is much smaller than the former, and therefore, in the present invention, the total of both latent heats is referred to as the latent heat of condensation of ethylene.
In the production method of the present invention, since vinyl acetate cooled to-50 to 23 ℃ is supplied to the heat exchanger, the temperature difference between the refrigerant supplied to the heat exchanger and vinyl acetate is small, and sensible heat of cooling by vinyl acetate is smaller than that in the case of supplying vinyl acetate at normal temperature. However, vinyl acetate easily dissolves ethylene due to low temperature, and thus the latent heat of condensation using ethylene increases. The inventors have conducted studies to find that the increase in latent heat is far more than the decrease in sensible heat, and that the latent heat is much larger even if the decrease in sensible heat when vinyl acetate is cooled before being supplied to the heat exchanger is subtracted. That is, by cooling the vinyl acetate supplied to the heat exchanger, the heat removal efficiency can be improved in terms of the entire system. This shows that the heat removal efficiency is improved by supplying only cooled vinyl acetate without changing the heat exchanger.
The structure of the heat exchanger is not particularly limited, and a wet wall heat exchanger is preferable because the contact area between the heat exchanger and vinyl acetate is large and the contact area between vinyl acetate and ethylene gas is also large. Thereby, it is possible to effectively deprive heat of vinyl acetate flowing down at a thin thickness on the surface of the wall while efficiently condensing and dissolving ethylene gas on the surface of vinyl acetate. The shape of the wall is not particularly limited, and is preferably in a state where vinyl acetate flows down among a large number of pipes. The number, diameter, length, etc. of the pipes can be set in consideration of the required heat removal amount, etc.
The vinyl acetate to ethylene contact process in the heat exchanger is believed to be by both co-current and counter-current contact. The co-current contact method is a method in which a pressurized gas containing ethylene is supplied to the upper part of a heat exchanger, and the pressurized gas containing ethylene and vinyl acetate are brought into co-current contact with each other in the heat exchanger. The countercurrent contact method is a method in which a pressurized gas containing ethylene is supplied to a lower part of the heat exchanger, and the pressurized gas containing ethylene is brought into countercurrent contact with vinyl acetate in the heat exchanger. Hereinafter, the description will be given separately.
In the co-current contacting method, both pressurized gas containing ethylene and vinyl acetate are introduced into the upper part of the heat exchanger. Both of them proceed downward, and ethylene is absorbed by vinyl acetate. Since the direction of travel is the same, the so-called flooding phenomenon, in which the vinyl acetate is lifted upward by the gas and flows backward, does not occur, and stable operation is easily maintained. Moreover, the improvement in heat removal efficiency by cooling vinyl acetate is significant compared to the convective contact approach, and the benefits of using the process of the present invention are large.
On the other hand, in the convection contact method, vinyl acetate is supplied to the upper part of the heat exchanger, and a pressurized gas containing ethylene is introduced to the lower part of the heat exchanger. When vinyl acetate flows downward, ethylene gas that has traveled upward is absorbed by the vinyl acetate. Each traveling in the opposite direction, and therefore, flooding may occur. Further, when the pressure in the polymerization vessel is high, the amount of gas flowing into the heat exchanger increases, and there is a possibility that scales adhere to the inside of the heat exchanger due to droplets of the reaction liquid.
The preparation method of the EVA of the invention comprises the following steps: and a step of introducing vinyl acetate in which ethylene is dissolved from the bottom of the heat exchanger and adding the vinyl acetate to the reaction solution in the polymerization vessel. By adding low-temperature vinyl acetate in which ethylene is dissolved to the reaction solution, ethylene is dissolved in the reaction solution while cooling the reaction solution. When ethylene dissolved in the reaction solution evaporates, the latent heat of evaporation is taken out from the reaction solution, and heat can be removed from the reaction solution. In this way, the reaction temperature can be maintained constant. The temperature of the ethylene-containing vinyl acetate is suitably from-10 to 40 ℃. The temperature is more preferably from-5 ℃ to 30 ℃.
The preparation method of the EVA of the invention comprises the following steps: and a step of taking out the reaction solution from the polymerization vessel. As described above, ethylene, vinyl acetate, a polymerization initiator, and methanol were continuously supplied to the reaction solution in the polymerization tank, and ethylene and vinyl acetate were consumed to produce EVA. The reaction solution having a predetermined polymerization rate is continuously withdrawn from the polymerization vessel. The polymerization rate of vinyl acetate is set in consideration of production efficiency, polymerization degree, and the like, and is preferably 25 to 60%, more preferably 30 to 50%.
The ethylene content of the obtained EVA is preferably 15-55 mol%. If the ethylene pressure in the polymerization vessel is high, EVA having a high ethylene content is obtained, and if the ethylene pressure in the polymerization vessel is low, EVA having a low ethylene content is obtained. When the ethylene content of EVOH obtained by saponifying EVA is low, gas barrier properties become good, but moldability is lowered. Conversely, when the ethylene content is high, the gas barrier property is lowered, but the moldability becomes good. Therefore, it is necessary to adjust the ethylene content to a preferable ethylene content in consideration of the use of EVOH and the like. The ethylene content is more preferably 45 mol% or less, still more preferably 40 mol% or less, and particularly preferably 35 mol% or less. On the other hand, if the heat removal efficiency is taken into consideration, a high ethylene content is advantageous, and the ethylene content is more preferably 20 mol% or more, and still more preferably 25 mol% or more.
The polymerization degree of the obtained EVA is preferably 500-2000. The formability and strength required for EVOH are appropriately set in consideration of the properties. The polymerization degree of EVA is suitably 600 or more, more suitably 700 or more. The polymerization degree of EVA is suitably 1600 or less, more suitably 1200 or less. Since the polymerization degree decreases if the methanol content in the reaction solution is high, and increases if the methanol content is low, the polymerization degree of the EVA to be obtained can be adjusted by adjusting the methanol content in the reaction solution.
The EVA obtained in this way can be used directly for various applications, and it is preferable to prepare EVOH by saponifying it. The method of saponification is not particularly limited, and a known method of hydrolysis in the presence of an alkali catalyst can be employed.
Hereinafter, a specific polymerization apparatus and a polymerization method using the same will be described with reference to the drawings. Fig. 1 is a schematic view of an apparatus used in example 1, and is an apparatus capable of bringing vinyl acetate and ethylene into co-current contact in a heat exchanger.
The polymerization tank 1 is connected to a plurality of pipes 5, 6, 7. The number and arrangement of the conduits are not limited to those shown in the drawings. Through these conduits, ethylene, a polymerization initiator, and methanol are supplied to the polymerization tank 1. In some cases, a part of the vinyl acetate and other monomers may be supplied through these conduits. In order to ensure the uniformity of the reaction solution, it is preferable to provide a stirrer 8 in the polymerization vessel 1 to stir the reaction solution. The reaction liquid in the polymerization vessel 1 is continuously discharged from a reaction liquid outlet pipe 9 connected to the bottom of the polymerization vessel 1. The polymerization vessel 1 is surrounded by a jacket (not shown) through which cooling water circulates.
A vinyl acetate inlet pipe 10 is connected to the heat exchanger 2, and vinyl acetate is supplied to the upper part of the heat exchanger 2 through the vinyl acetate inlet pipe. From the viewpoint of heat removal efficiency, it is preferable to supply the total amount of vinyl acetate supplied to the polymerization vessel 1 from the vinyl acetate introduction pipe 10 via the heat exchanger 2, but a part of the vinyl acetate may be directly supplied to the polymerization vessel 1 from the conduits 5, 6, and 7 directly connected to the polymerization vessel 1 within a range not to impair the effect of the present invention.
The heat exchanger 2 is connected to refrigerant pipes 11 and 12. The position of the tube is not limited to the illustrated embodiment, and the refrigerant is preferably supplied from the refrigerant tube 12 connected to the lower portion of the heat exchanger 2 and discharged from the refrigerant tube 11 connected to the upper portion of the heat exchanger 2. By connecting in this manner, vinyl acetate can be efficiently cooled, and the heat removal efficiency from the reaction solution is good. The cooling medium is not particularly limited, and an aqueous alcohol solution such as methanol, ethanol, ethylene glycol, or glycerol, an aqueous solution of salt or calcium chloride, or freon can be used. An aqueous alcohol solution, particularly an aqueous methanol solution, is preferably used for reasons of ease of handling, cost, and the like.
A gas discharge pipe 13 for discharging gas from the heat exchanger 2 is connected to a lower portion of the heat exchanger 2. A mist separator (not shown) may be connected to the gas discharge pipe 13. The droplets in the exit gas are removed by a mist separator, enabling the recovery or release of ethylene in the absence of mist. The mist separator is a device for separating droplets floating in a gas by utilizing an external force such as gravity, seed, centrifugal force, or electrostatic force, or by utilizing a shielding or screening effect. Examples of the mist separator include a gravity settler, a cyclone separator, an electric dust collector, a cleaning tower, a bag-type dust collector, and a packed bed. Among these, a cyclone separator is preferable.
2 pipes 3 and 4 connect the polymerization tank 1 and the heat exchanger 2. Ethylene-containing gas is introduced from the polymerization reactor 1 through the conduit 3 into the upper part of the heat exchanger 2, and ethylene-absorbed vinyl acetate is introduced from the lower part of the heat exchanger 2 through the conduit 4 into the polymerization reactor 1.
Vinyl acetate as a raw material is supplied to the heat exchanger 2 through a vinyl acetate inlet pipe 10. The vinyl acetate supplied to the upper portion of the heat exchanger 2 absorbs ethylene while passing through the heat exchanger 2. Vinyl acetate effectively removes the heat of polymerization by absorbing ethylene. In this case, it is important to supply vinyl acetate cooled to-50 to 23 ℃. By supplying the vinyl acetate cooled in advance, heat can be removed in the heat exchanger 2 with good efficiency.
The ethylene-containing gas is introduced into the heat exchanger 2 through a conduit 3 connected to the upper part of the heat exchanger 2. The heat exchanger-side conduit 3 and the vinyl acetate inlet pipe 10 are connected to the upper part of the heat exchanger 2. By connecting the conduit 3 to the upper part of the heat exchanger, overflow of vinyl acetate can be suppressed even when the supply amount of the ethylene-containing gas is increased. As described above, the ethylene-containing gas is brought into contact with the vinyl acetate and simultaneously descends in the heat exchanger 2 in parallel with the ethylene-containing liquid. As a result, ethylene in the gas is dissolved in vinyl acetate.
The vinyl acetate-containing liquid having absorbed ethylene is introduced into the polymerization vessel 1 through the conduit 4. Further, the heat of polymerization can be removed by evaporating ethylene from the reaction solution. In the case of continuous production, ethylene is circulated through the polymerization tank 1, the heat exchanger 2 and the conduits 3, 4. Since a part of ethylene is contained in EVA and discharged from the reaction solution delivery pipe 9, it is replenished from an ethylene supply source connected to the polymerization tank 1 through at least 1 of the conduits 5, 6, and 7.
FIG. 2 is a schematic view of an apparatus used in example 2, which is an apparatus capable of bringing vinyl acetate and ethylene into convective contact in a heat exchanger. Since most of the apparatus is common to the apparatus of the parallel flow contact system shown in fig. 1, only the difference will be described below.
2 conduits 3, 4 connect the polymerization tank 1 and the heat exchanger 2, but the location where the conduit 3 is connected to the heat exchanger 2 is different from the apparatus of FIG. 1. Thereby, the ethylene-containing gas is introduced from the polymerization vessel 1 through the conduit 3 into the lower part of the heat exchanger 2, and the vinyl acetate-containing liquid having absorbed ethylene is introduced from the lower part of the heat exchanger 2 through the conduit 4 into the polymerization vessel 1. By connecting the conduit 3 to the lower part of the heat exchanger, the ethylene-containing gas rises in the heat exchanger and comes into contact with the vinyl acetate-containing liquid flowing down in a countercurrent manner, whereby ethylene in the gas is dissolved in the vinyl acetate-containing liquid. Further, a gas discharge pipe 13 for discharging gas from the heat exchanger 2 is connected to an upper portion of the heat exchanger 2.
Examples
Example 1
EVA was continuously produced using a co-current contact polymerization apparatus as shown in FIG. 1. A polymerization reactor 1 having an internal volume of 750L and a heat transfer area of 4m were prepared2And a vertical wet-wall multi-tube heat exchanger 2 having 10 tubes. Hereinafter, an example of the production of EVA having an ethylene content of 24.0 mol% and a polymerization degree of 1080 by supplying vinyl acetate at-20 ℃ will be described.
Pressurized ethylene was supplied from the conduit 5 to the polymerization reactor 1 so as to maintain the pressure in the polymerization reactor 1 at 2.9 MPa. The ethylene content of the EVA obtained can be controlled by adjusting the pressure in the polymerization tank 1. 2,2' -azobis- (4-methoxy-2, 4-dimethylvaleronitrile), which is a polymerization initiator, was introduced into the polymerization vessel 1 through the conduit 6 at a rate of 3g/hr as a methanol solution. Further, methanol is introduced into the polymerization vessel 1 through a conduit 7. The introduction rate of methanol was 6.2kg/hr in total of the introduction rates from the conduit 6 and the conduit 7. The polymerization degree can be controlled by adjusting the content of methanol in the reaction solution.
Vinyl acetate (VAc) cooled to-20 ℃ was supplied to polymerization vessel 1 through vinyl acetate inlet pipe 10 and heat exchanger 2 at a rate of 70.6 kg/hr. The ethylene-containing gas in the polymerization vessel 1 is introduced into the heat exchanger 2 through the conduit 3. Vinyl acetate flows down the surface of the tubes in the same direction as the ethylene-containing gas in heat exchanger 2. The temperature of the ethylene-containing vinyl acetate having absorbed ethylene after flowing down was 8 ℃, and the ethylene-containing vinyl acetate was introduced into the polymerization vessel 1 through the conduit 4 and mixed with the reaction solution. In the reaction solution, ethylene and vinyl acetate were continuously polymerized, and a polymerization solution containing EVA was continuously obtained from the pipe 9. The temperature of the reaction solution in the polymerization vessel 1 was maintained at 60 ℃.
During the reaction, a 30 wt% aqueous methanol solution at-5 ℃ was supplied through conduit 12 and discharged through conduit 11 as a cooling medium. In the heat exchanger 2, the cooling medium is supplied so as to flow in the opposite direction to the vinyl acetate. The amount of heat removed by heat exchanger 2 was 6803 kcal/hr. Further, cooling water is circulated through a jacket covering the polymerization vessel 1, and the jacket is cooled from the outside of the polymerization vessel 1. The circulation speed of the cooling water is constant at all times. The polymerization rate of vinyl acetate in the obtained polymerization solution was 40%. The ethylene content of the ethylene-vinyl acetate copolymer (EVA) obtained was 24.0 mol%, and the degree of polymerization was 1080. A summary of these results is shown in Table 1.
As shown in example 1 of Table 1, the same tests as described above were carried out while changing the temperature of vinyl acetate supplied from conduit 10 to 0 ℃, 5 ℃, 10 ℃, 20 ℃ and 25 ℃. At this time, the temperature of the reaction liquid in the polymerization vessel 1 was maintained at 60 ℃, and the temperature of the ethylene-containing vinyl acetate injected into the polymerization vessel 1 from the conduit 4 was maintained at 8 ℃. In addition, various conditions were adjusted so as to obtain EVA having a polymerization degree of vinyl acetate of 40%, an ethylene content of 24.0 mol%, and a polymerization degree of 1080. The amount of the polymerization initiator introduced was changed in proportion to the square of the amount of vinyl acetate supplied. The temperature of the ethylene-containing vinyl acetate introduced into the polymerization vessel 1 was maintained at 8 ℃ and the temperature of the polymerization vessel was maintained at 60 ℃ by controlling the circulation rate of the refrigerant supplied from the conduit 12 and the amount of vinyl acetate introduced from the conduit 10. As a result, vinyl acetate was supplied from the conduit 10 in an amount shown in table 1, and the heat shown in table 1 was removed in the heat exchanger 2.
From the results of example 1, it is understood that the supply amount of vinyl acetate can be increased and the heat removal amount in the heat exchanger 2 can be greatly increased by lowering the temperature of vinyl acetate supplied from the conduit 10. The temperature of the supplied vinyl acetate was reduced from 25 ℃ to-20 ℃ and the heat removal increased significantly from 3453kcal/hr to 6803 kcal/hr. The difference (A) between the heat removal amounts when vinyl acetate was supplied at 25 ℃ and when vinyl acetate was supplied at-20 ℃ was 3351 kcal/hr. Here, the difference (B) in the amount of heat removed in advance by lowering the temperature of the vinyl acetate supplied from the conduit 10 is 1359kcal/hr, and therefore the difference ((a) - (B))1992kcal/hr is an increase in the amount of substantial heat removal caused by lowering the temperature of the vinyl acetate supplied. As can be seen, by decreasing the temperature of the supplied vinyl acetate, the heat removal amount was significantly increased. Further, the supply amount of vinyl acetate was significantly increased from 36.1kg/hr to 70.6kg/hr, and productivity was also significantly improved.
Examples 2 to 8
EVA having ethylene content and polymerization degree shown in table 1 and table 2 was polymerized in the same manner as in example 1. The refrigerant temperature was fixed at-5 ℃ and the polymerization temperature was fixed at 60 ℃ respectively. The polymerization rate of vinyl acetate and the temperature of vinyl acetate containing ethylene were set to values shown in tables 1 and 2, and the temperature of vinyl acetate supplied from conduit 10 was changed to-20 ℃, 0 ℃, 5 ℃, 10 ℃, 20 ℃ and 25 ℃. The pressure in the polymerization vessel 1, the vinyl acetate feed amount, and the heat removal amount under each condition are summarized in tables 1 and 2. It is known that even in the case of polymerizing EVA having different ethylene contents and polymerization degrees, by lowering the temperature of supplied vinyl acetate, the heat removal amount is significantly increased, while the productivity is significantly improved.
Example 9
EVA was continuously produced using a polymerization apparatus of the convection contact type shown in FIG. 2. This experimental apparatus was the same-sized apparatus except that the positions of the conduit 3 and the gas discharge pipe 13 connected to the heat exchanger 2 were different in the parallel-flow contact type manufacturing apparatus used in example 1. Hereinafter, an example of preparing EVA having an ethylene content of 24.0 mol% and a polymerization degree of 1080 by introducing vinyl acetate at-20 ℃ will be described.
Pressurized ethylene was supplied from the conduit 5 to the polymerization reactor 1 so as to maintain the pressure in the polymerization reactor 1 at 2.9 MPa. The ethylene content of the EVA obtained can be controlled by adjusting the pressure in the polymerization tank 1. 2,2' -azobis- (4-methoxy-2, 4-dimethylvaleronitrile), which is a polymerization initiator, was introduced into the polymerization vessel 1 through the conduit 6 at a rate of 3g/hr as a methanol solution. Further, methanol is introduced into the polymerization vessel 1 through a conduit 7. The introduction rate of methanol was 4.4kg/hr in total of the introduction rates from the conduit 6 and the conduit 7. The polymerization degree can be controlled by adjusting the content of methanol in the reaction solution.
Vinyl acetate (VAc) cooled to-20 ℃ was supplied to polymerization vessel 1 through vinyl acetate inlet pipe 10 and heat exchanger 2 at a rate of 75.0 kg/hr. The ethylene-containing gas in the polymerization vessel 1 is introduced into the heat exchanger 2 through the conduit 3. Vinyl acetate flows down the surface of the tubes in the heat exchanger 2 in a direction opposite to the flow of the ethylene-containing gas. The temperature of the ethylene-containing vinyl acetate having absorbed ethylene after flowing down was 2 ℃, and the ethylene-containing vinyl acetate was introduced into the polymerization vessel 1 through the conduit 4 and mixed with the reaction solution. In the reaction solution, ethylene and vinyl acetate were continuously polymerized, and a polymerization solution containing EVA was continuously obtained from the pipe 9. The temperature of the reaction solution in the polymerization vessel 1 was maintained at 60 ℃.
During the reaction, a 30 wt% aqueous methanol solution at-5 ℃ was supplied through conduit 12 and discharged through conduit 11 as a cooling medium. In the heat exchanger 2, the cooling medium is supplied so as to flow in the opposite direction to the vinyl acetate. The amount of heat removed by heat exchanger 2 was 5647 kcal/hr. Further, cooling water is circulated through a jacket covering the polymerization vessel 1, and the jacket is cooled from the outside of the polymerization vessel 1. The circulation speed of the cooling water is constant at all times. The polymerization rate of vinyl acetate in the obtained polymerization solution was 40%. The ethylene content of the ethylene-vinyl acetate copolymer (EVA) obtained was 24.0 mol%, and the degree of polymerization was 1080.
As shown in example 9 of Table 3, the same tests as described above were carried out while changing the temperature of the vinyl acetate supplied from the conduit 10 to 0 ℃, 5 ℃, 10 ℃, 20 ℃ and 25 ℃. At this time, the temperature of the reaction liquid in the polymerization vessel 1 was maintained at 60 ℃, and the temperature of the ethylene-containing vinyl acetate injected into the polymerization vessel 1 from the conduit 4 was maintained at 2 ℃. In addition, various conditions were adjusted so as to obtain EVA having a polymerization degree of vinyl acetate of 40%, an ethylene content of 24.0 mol%, and a polymerization degree of 1080. The amount of the polymerization initiator introduced was changed in proportion to the amount of vinyl acetate supplied. The temperature of the ethylene-containing vinyl acetate supplied to the polymerization vessel 1 was maintained at 2 ℃ and the temperature of the polymerization vessel was maintained at 60 ℃ by controlling the circulation rate of the refrigerant supplied from the conduit 12 and the amount of vinyl acetate supplied from the conduit 10. As a result, vinyl acetate was supplied from conduit 10 in an amount shown in table 3, and the heat shown in table 3 was removed in heat exchanger 2.
From the results of example 9, it is understood that the supply amount of vinyl acetate can be increased and the heat removal amount in the heat exchanger 2 can also be increased by lowering the temperature of vinyl acetate supplied from the conduit 10. The temperature of the supplied vinyl acetate was lowered from 25 ℃ to-20 ℃ and the heat removal amount was increased from 3847kcal/hr to 5647 kcal/hr. The difference (A) between the heat removal amounts when vinyl acetate was supplied at 25 ℃ and when vinyl acetate was supplied at-20 ℃ was 1800 kcal/hr. Here, since the difference (B) in the amount of heat removed in advance is 1445kcal/hr by lowering the temperature of the vinyl acetate supplied from the conduit 10, the difference ((a) - (B)) of the amount of heat removed is an increase in the amount of substantial heat removal caused by lowering the temperature of the supplied vinyl acetate. As can be seen, the heat removal amount is increased by lowering the temperature of the supplied vinyl acetate. Further, the supply amount of vinyl acetate was increased from 51.4kg/hr to 75.0kg/hr, and the productivity was also improved.
Examples 10 to 16
In the same manner as in example 9, EVA having the ethylene content and the degree of polymerization shown in tables 3 and 4 was polymerized. The refrigerant temperature was fixed at-5 ℃ and the polymerization temperature was fixed at 60 ℃ respectively. The polymerization rate of vinyl acetate and the temperature of vinyl acetate containing ethylene were set to values shown in tables 3 and 4, and the temperature of vinyl acetate supplied from conduit 10 was changed to-20 ℃, 0 ℃, 5 ℃, 10 ℃, 20 ℃ and 25 ℃. The pressure in the polymerization vessel 1, the vinyl acetate feed amount, and the heat removal amount under each condition are summarized in tables 3 and 4. It is known that even in the case of polymerizing EVA having different ethylene contents and polymerization degrees, by lowering the temperature of supplied vinyl acetate, the amount of heat removal increases, while productivity also improves.
As is clear from comparison of tables 1 to 4, the difference ((A) to (B)) between the heat removal amounts substantially in the case where the temperature of vinyl acetate is 25 ℃ is larger in the co-current contact polymerization apparatus than in the case where the temperature is 25 ℃. Therefore, it is found that the parallel flow type polymerization apparatus is more advantageous in supplying vinyl acetate at a lower temperature than the flow type polymerization apparatus.
Description of the reference numerals
1 polymerization tank
2 Heat exchanger
3 to 7 guide tube
8 stirring machine
9 reaction liquid leading-out pipe
10 vinyl acetate inlet pipe
11. 12 refrigerant pipe
13 gas discharge pipe
Claims (6)
1. A method for producing an ethylene-vinyl acetate copolymer, wherein the ethylene-vinyl acetate copolymer is continuously produced in a polymerization tank containing a reaction liquid containing ethylene, vinyl acetate, a polymerization initiator, and methanol, and the polymerization tank is connected to a heat exchanger for circulating a refrigerant via a pipe; the method is characterized by comprising the following steps:
supplying ethylene, a polymerization initiator and methanol to the polymerization vessel;
introducing a pressurized gas containing ethylene present in the gas phase portion of the polymerization vessel into the heat exchanger;
supplying vinyl acetate cooled to-50 to 23 ℃ to the upper part of the heat exchanger;
a step in which ethylene is absorbed in the vinyl acetate while flowing down in the aforementioned heat exchanger;
a step of introducing vinyl acetate in which ethylene is dissolved from the bottom of the heat exchanger and adding the vinyl acetate to the reaction solution in the polymerization vessel; and
and a step of taking out the reaction solution from the polymerization vessel.
2. The production method according to claim 1, wherein vinyl acetate cooled to-50 to 10 ℃ is supplied to an upper part of the heat exchanger.
3. The production method according to claim 1 or 2, wherein the pressurized gas containing ethylene is supplied to an upper portion of the aforementioned heat exchanger, and the pressurized gas containing ethylene is brought into co-current contact with vinyl acetate in the heat exchanger.
4. The production process according to claim 1 or 2, wherein the pressurized gas containing ethylene is supplied to a lower portion of the aforementioned heat exchanger, and the pressurized gas containing ethylene is brought into counter-current contact with vinyl acetate in the heat exchanger.
5. The production method according to claim 1 or 2, wherein the ethylene content of the obtained ethylene-vinyl acetate copolymer is 15 to 55 mol%.
6. The production method according to claim 1 or 2, wherein the heat exchanger is a wetted wall heat exchanger.
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| JP2018104045 | 2018-05-30 | ||
| JP2018-104045 | 2018-05-30 | ||
| PCT/JP2019/021253 WO2019230781A1 (en) | 2018-05-30 | 2019-05-29 | Method for producing ethylene-vinyl acetate copolymer |
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| US (1) | US11535685B2 (en) |
| CN (1) | CN110709434B (en) |
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| CN114181333B (en) * | 2020-09-15 | 2024-01-26 | 中国石油化工股份有限公司 | Method and device for preparing ethylene-vinyl acetate copolymer |
| CN113105574A (en) * | 2021-04-12 | 2021-07-13 | 江苏斯尔邦石化有限公司 | Ethylene-vinyl acetate copolymer and preparation method and application thereof |
| CN115991810A (en) * | 2021-10-19 | 2023-04-21 | 中国石油化工股份有限公司 | EPVA polymerization heat removal method under low pressure condition, and EPVA preparation method and EPVA preparation device |
| CN114230700B (en) * | 2022-01-07 | 2022-10-04 | 云南正邦科技有限公司 | Method for preparing high-ethylene-content EVA copolymer through medium and low pressure solution polymerization |
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| JPS6053513A (en) * | 1983-09-01 | 1985-03-27 | Kuraray Co Ltd | Process for continuous production of ethylene-vinyl acetate copolymer |
| CN1088942A (en) * | 1992-11-26 | 1994-07-06 | 埃勒夫阿托化学有限公司 | The low molecular mass ethylene-vinyl acetate copolymers preparation method |
| JPH11116637A (en) * | 1997-10-09 | 1999-04-27 | Nippon Synthetic Chem Ind Co Ltd:The | Polymerization of ethylene-vinyl acetate copolymer |
| JP2000198803A (en) * | 1999-01-08 | 2000-07-18 | Nippon Synthetic Chem Ind Co Ltd:The | Production of ethylene-vinyl acetate copolymer |
| TWI258484B (en) * | 2001-03-30 | 2006-07-21 | Kuraray Co | Preparation of ethylene-vinyl acetate copolymer and preparation device |
| TWI309242B (en) * | 2001-03-16 | 2009-05-01 | Kuraray Co | Method for the production of ethylene-vinyl acetate copolymer |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2300111C3 (en) * | 1973-01-03 | 1984-10-25 | Basf Ag, 6700 Ludwigshafen | Process for removing the heat of reaction in the copolymerization of ethylene in an aqueous dispersion |
| TW366351B (en) | 1994-12-26 | 1999-08-11 | Mitsui Chemicals Inc | Production process of acrylonitrile (co)polymers |
| JP3645342B2 (en) * | 1994-12-26 | 2005-05-11 | 三井化学株式会社 | Method for producing acrylonitrile-based (co) polymer |
| JP4700183B2 (en) | 2000-10-27 | 2011-06-15 | 日本合成化学工業株式会社 | Process for producing ethylene-vinyl acetate copolymer |
| JP4213394B2 (en) | 2001-03-16 | 2009-01-21 | 株式会社クラレ | Method and apparatus for producing ethylene-vinyl acetate copolymer |
| JP3759467B2 (en) | 2001-03-30 | 2006-03-22 | 株式会社クラレ | Manufacturing method and manufacturing apparatus of ethylene-vinyl acetate copolymer |
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2019
- 2019-05-27 TW TW108118180A patent/TWI810303B/en active
- 2019-05-29 CN CN201980002312.7A patent/CN110709434B/en active Active
- 2019-05-29 SG SG11202011826UA patent/SG11202011826UA/en unknown
- 2019-05-29 US US17/059,566 patent/US11535685B2/en active Active
- 2019-05-29 WO PCT/JP2019/021253 patent/WO2019230781A1/en unknown
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6053513A (en) * | 1983-09-01 | 1985-03-27 | Kuraray Co Ltd | Process for continuous production of ethylene-vinyl acetate copolymer |
| CN1088942A (en) * | 1992-11-26 | 1994-07-06 | 埃勒夫阿托化学有限公司 | The low molecular mass ethylene-vinyl acetate copolymers preparation method |
| JPH11116637A (en) * | 1997-10-09 | 1999-04-27 | Nippon Synthetic Chem Ind Co Ltd:The | Polymerization of ethylene-vinyl acetate copolymer |
| JP2000198803A (en) * | 1999-01-08 | 2000-07-18 | Nippon Synthetic Chem Ind Co Ltd:The | Production of ethylene-vinyl acetate copolymer |
| TWI309242B (en) * | 2001-03-16 | 2009-05-01 | Kuraray Co | Method for the production of ethylene-vinyl acetate copolymer |
| TWI258484B (en) * | 2001-03-30 | 2006-07-21 | Kuraray Co | Preparation of ethylene-vinyl acetate copolymer and preparation device |
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| US20210230314A1 (en) | 2021-07-29 |
| TW202003589A (en) | 2020-01-16 |
| WO2019230781A1 (en) | 2019-12-05 |
| US11535685B2 (en) | 2022-12-27 |
| CN110709434A (en) | 2020-01-17 |
| TWI810303B (en) | 2023-08-01 |
| SG11202011826UA (en) | 2020-12-30 |
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